This invention relates to the manufacture of shims, and, more particularly, to the manufacture of shims from cellulosic fiberboard.
Shims are used in a variety of manufacturing operations to fill unwanted gaps or spaces in assembled articles, caused by imperfectly fitting components. For example, in the automotive industry, steel shims are commonly used to fill gaps during the assembly of automotive chassis, in the front suspension, cowl, and bumper areas. These shims are of various sizes and shapes and typically range from about 1 to 100 square inches in area and from about 1/16 inch to as much as 1/2 inch in thickness. Frequently more than one shim is required to fill a particular gap, the shims being tapped into place edgewise.
Steel shims have several disadvantages. They are relatively heavy and costly to produce, and they tend to rattle in service. Shims manufacture from a fiberboard material, formed of cellulose fibers bonded together by and impregnated with a suitable resin such as phenol impregnated board, overcome the aforementioned disadvantages of steel shims in that the fiber-board shims are less costly to produce, the have a lower bulk density than steel, and provide a sound deadening effect as compared to steel. However, fiberboard shims tend to deform and delaminate seriously as they are being tapped into place. Moreover, they tend to shrink during use, which then permits movement of the assembled components and which causes bolts running through the shims to lose their torque. Fiberboard shims are also relatively easily compressed and tend to absorb moisture during use.
Accordingly, it is among the principal objects of this invention to provide a method of making cellulosic fiberboard shims to overcome the aforementioned disdvantages of steel shims, and to provide shims which are relatively light weight but are dense, hard and strong and essentially chemical and moisture resistant.